Resin composition for lens sheet, lens sheet, and projection screen

ABSTRACT

Provided is a resin composition for lens sheet, a lens sheet, and a projection screen which by defining the mechanical properties based on the consideration of the pressure and time factor actually applied to an ionizing radiation curable resin enables obtaining excellent images without, even if any pressure has been applied to the lens sheet surface, causing crush of the configuration of the lens. The lens sheet is molded using an ionizing radiation curable resin composition in which the compression modulus of elasticity is greater than 0 MPa and smaller than 840 MPa and the creep deformation factor is greater than 0% and smaller than 57%; or the compression modulus of elasticity is greater than 840 MPa and smaller than 3500 MPa and the creep deformation factor is greater than −10% and smaller than 20%; or when E (MPa) represents the compression modulus of elasticity and C (%) represents the creep deformation factor, the ionizing radiation curable resin composition has a compression modulus of elasticity and creep deformation factor that have the relationship of 
     C&lt;−2×10 −2 E+63 and C&gt;−2.6×10 −3 E+3

TECHNICAL FIELD

[0001] The present invention relates to an ionizing radiation curableresin composition that forms a lens sheet such as a Fresnel lens sheet,a lens sheet whose lens portion has been formed using that composition,and a projection screen that is equipped with that lens sheet.

BACKGROUND ART

[0002] Up to now, a two-sheet structure of projection screen that hasbeen prepared by combining a lenticular lens and a Fresnel lens witheach other is general as the projection screen. In this structure, tobond the both lenses to each other, it is practiced to assemble alenticular lens sheet, which has been warped beforehand, to a planarFresnel lens sheet in such a way as to press the former lens sheetagainst the latter lens sheet as illustrated in FIG. 1. Accordingly, apressure is produced at a portion of contact between the assembled bothlens sheets. For example, as illustrated in FIG. 6, in the case of ascreen in which the lens surface of the lenticular lens the ridge ofthat has been vertically formed has been superposed upon the lenssurface of the circular Fresnel lens, at the left and right parts of thescreen line contacts mainly occur while at the vertical end parts of thescreen mainly point contacts occur. In this projection screen, on theside of the Fresnel lens sheet that opposes the lenticular lens sheet,the portions each of that is substantially triangular in cross sectionand each apex point of that sharpens are concentrically arrayed. In thesurface of the lenticular lens sheet that opposes the Fresnel lenssheet, the cross-sectional configuration thereof is formed into asemi-circular-columnar configuration. Accordingly, the material (resincomposition) constituting the lens surface of the Fresnel lens sheethaving the sharpening forward ends at their portions of contact needs tohave a predetermined value or more of mechanical property with respectto the crush. This is because in case the lens surface is easily crushedwith the above-described pressure, when that lens sheet has been used asthe projection screen, excellent images cannot be obtained.

[0003] With respect to the above-described problems, in thespecification of Japanese Patent Application Laid-Open No. 10-10647,there is disclosed a lens sheet the configuration stability of that isexcellent over a wide temperature range and the optical properties ofthat can be maintained as are by setting the elastic modulus of theactive energy radiation curable resin used in the lens portion of thelens sheet to be in the range of from 80 to 20000 kg/cm² within atemperature range of from −20 to +40° C.

[0004] Also, in Japanese Patent Application No. 2000-036435, thedissipation factor tan δ of the dynamic visco-elasticity after curing ofthe ionizing radiation curable resin constituting the lens is set tofall within a predetermined range considering a case where dynamic forcehas been applied to the lens sheet to thereby provide a resincomposition for lens sheet that has no strain built therein,flexibility, and excellent restorability.

[0005] However, in the specification of the above-described JapanesePatent Application Laid-Open No. 10-10647, the elastic modulus that isdefined in JIS K-7113 is adopted. This elastic modulus is the one thatis obtained by determining the value of the tensile elastic modulusthrough the use of a flat film, and therefore cannot be said to be theone that faithfully reproduces in an environment where. an actualionizing radiation curable resin is placed (receives a compressionforce).

[0006] Also, the pressure that when the resin composition is actuallyused as the projection screen occurs between the both lenses has a greatlength of duration. Namely, part of the resin composition for lens has arestoration force that acts to press that pressure back by degrees.Accordingly, when designing and selecting the resin composition forlens, it is necessary to take a time factor into consideration thatshould be involved in the mechanical properties of the resincomposition.

DISCLOSURE OF THE INVENTION

[0007] Thereupon, the present invention has an object to provide a resincomposition for lens sheet, the lens sheet, and a projection screenusing it, which, by defining the mechanical properties based on theconsideration of the pressure and time factor an ionizing radiationcurable resin composition actually receives, even when any pressure isapplied to the surface of the lens sheet, can obtain excellent imageswithout having the lens configuration crushed due to that pressure.

[0008] Hereinafter, the present invention will be explained. In anaspect of the present invention, the above-described problems are solvedby an ionizing radiation curable resin composition, the ionizingradiation curable resin composition forming a lens portion of a lenssheet, wherein the compression modulus of elasticity is greater than 0MPa and smaller than 840 MPa; and the creep deformation factor isgreater than 0% and smaller than 57%. The “elastic modulus” and “creepdeformation factor” referred to here each mean a value that has beenobtained by measurement performed using a “small degree of hardnesstester” that will be described later.

[0009] Also, in a second aspect of the present invention, theabove-described problems are solved by an ionizing radiation curableresin composition, the ionizing radiation curable resin compositionforming a lens portion of a lens sheet, wherein the compression modulusof elasticity is greater than 840 MPa and smaller than 3500 MPa; and thecreep deformation factor is greater than −10% and smaller than 20%.

[0010] Further, in a third aspect of the present invention, theabove-described problems are solved by an ionizing radiation curableresin composition, the ionizing radiation curable resin compositionforming a lens portion of a lens sheet, wherein when E (MPa) representsthe compression modulus of elasticity and C (%) represents the creepdeformation factor, the ionizing radiation curable resin composition hasa compression modulus of elasticity and creep deformation factor thathave the relationship of

C<−2×10⁻² E+63 and C>−2.6×10⁻³ E+3

[0011] According to each of these aspects of the present invention, itis possible to obtain an ionizing radiation curable resin compositionthat in case it is used for molding a lens surface, even when anypressure is applied to the surface of the lens sheet, can obtainexcellent images without having the lens configuration crushed due tothat pressure.

[0012] In a fourth aspect of the present invention, the Fresnel lenssheet may be constructed as a Fresnel lens sheet whose lens surface isformed of the ionizing radiation curable resin composition as describedin one of the above-described aspects.

[0013] Further, in a fifth aspect of the present invention, theprojection screen may be constructed as a projection screen that isequipped with the Fresnel lens sheet according to the above-describedaspect.

[0014] The above-described functions and advantages of the presentinvention will be made clear from the embodiments that will be explainednext.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows three pieces of views each illustrating a state wherea lenticular lens sheet is assembled to a Fresnel lens sheet to therebyprepare a screen;

[0016]FIG. 2 is a graphic diagram illustrating a load/intrusion-depthcurve;

[0017]FIG. 3 is a view illustrating the position at which an indenter isintruded into a sample lens;

[0018]FIG. 4 is a graphic diagram illustrating the relationship of theelastic modulus/creep deformation factor to the evaluation on the crush;

[0019]FIG. 5 is a graphic diagram illustrating, when in FIG. 4 attentionis directed only towards the relationship between the two of the elasticmodulus E and the creep deformation factor C, the range that enablesobtaining a lens involving no problems with the crush;

[0020]FIG. 6 shows three pieces of views each illustrating acircumstance where when the Fresnel lens and the lenticular lens havebeen superposed one upon the other portions of contact occur; and

[0021]FIG. 7 is a view illustrating the load/the intrusion-depth curvethat has been obtained from the conducting of a universal-hardness test.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] As a result of having studied various testing methods, in orderto measure the mechanical properties additionally involving the timefactor of the ionizing radiation curable resin composition, the inventorof this application has found out that the small degree of hardnessmeasuring device is the most suitable. Also, by adopting the elasticmodulus (E) and creep deformation factor (C) as the measured valuesobtained by measurement performed using the above-described small degreeof hardness measuring device, the inventor has found out that it ispossible to selectively determine the ionizing radiation curable resincomposition for fresnel lens sheet that can be used with no problemsarising from the pressure that it receives when it is used in therelevant projection screen. Hereinafter, sequential explanations will begiven of the details of the small degree of hardness testing device, thetesting-sample-preparing method, the measuring conditions, the measuringitems, the crush evaluation on the Fresnel lens molded using theionizing radiation curable resin composition that has been used in theabove-described tests, the measured results of these tests, and theanalyses results thereof.

[0023] [Embodiments]

[0024] (1) Small degree of hardness testing device

[0025] The small degree of hardness testing device that is used in theembodiment of the present invention of this application is a type ofuniversal-hardness testing device and, in the market, is available asthe “Fisher' scope H-100V” produced by Fisher. This testing device isoriginally the one that presses an indenter into the surface of a sampleand directly reads the intruding depth of the recess in a state where apredetermined magnitude of load has been applied to thereby determinethe universal hardness. The inventor of this application, in thistesting device, caused the load applied to the indenter to vary underpredetermined conditions and measured various kinds of mechanicalproperties of the sample (resin composition). Using this testing device,it is possible to measure various kinds of properties (the propertiesvalues of the universal hardness HU, the plasticity hardness HU_(PLAST),the flow behavior, the creep behavior, the restoration of elasticitybehavior, etc.). In this testing device, as the indenter, a Vickerspyramid indenter the dimensional precision of that is high in particularis used, with the result that a load/intrusion-depth curve such as thatillustrated in FIG. 7 is measured. The measured data is processed by acomputer equipped to the tester, with the result that there are obtainedan “elastic deformation straight line”, such as indicated in a brokenline in the Figure, and a “amount of plastic deformation” hr' that isestimated therefrom and represents the intrusion depth under a testingload, such as that indicated in a broken line in the Figure. Further,not only the relationship between the universal hardness and theintrusion depth but also other relationship can be simply illustrated.Regarding the details of such theoretical mutual relationships betweenthe tested values, it is recommended to refer to the monthly publication“Material-Testing Technology” April issue, Vol. 43, No. 2, in the yearof 1998 and to the separate volume “Evaluation of Material Properties byUniversal-hardness Test” (Cornelia Heermant, Dieter Dengel (translated)by Katayama Shigeo and Satoh Shigeo).

[0026] Incidentally, this testing method is registered as the “TestingMethod on Metallic Materials” under a German Testing Standard (DINstandard) 50359-1. Also, there is a proposed standard that is defined asan ISO Standard and the Committee draft of that is published in 1999.

[0027] (2) Testing Sample Preparing Method

[0028] An ionizing radiation curable resin composition, which becomes asample, is coated onto a Fresnel lens molding die to a thickness of 200μm. The die temperature at this time is maintained at a temperature of40 to 42° C. while the resin temperature at a temperature of 42° C.Subsequently, ultraviolet rays are radiated onto the thus-coatedionizing radiation curable resin composition through the use of amolding lamp (the metal halide lamp: produced by Japan Storage BatteryCo., Ltd.) under the radiation condition that the UV dose is 2000mJ/cm²; and the peak intensity is 250 mW/cm², to thereby cure that resincomposition. It thereafter is exfoliated from the die and was used asthe testing sample.

[0029] (3) Measuring Conditions

[0030] While, as described above, in the test for universal-hardness,the indenter is pressed into the surface of the sample and, with theintrusion load being applied to it, the intrusion depth of the recess isread to thereby determine the hardness, the inventor of this applicationgradually increased or decreased the intrusion load based on the use ofthe indenter up to, or down to, a predetermined value and therebymeasured various kinds of mechanical properties of the sample resincomposition. Incidentally, here, as the indenter, there was used atungsten-carbide ball indenter having a diameter of 0.4 mm. Hereinafter,concrete measuring conditions will be explained with reference to FIG.2.

[0031] In FIG. 2, the point A indicates the state prior to the start ofthe test. Here in this position A, the load (ordinate axis) is notapplied and therefore has a value of 0, while the intrusion depth of theindenter (abscissa axis) is also similarly 0 in value. At the point A,the forward end of the lower end portion of the indenter is in a stateof very slightly contacting with the surface of the sample. The positionof the forward end of the lower end portion of the indenter was set,while it is being confirmed using a microscope, so that it may fall uponthe center position of the lens-section length in the vicinity 2 to 3 mmaway from the center of the Fresnel lens sample (see FIG. 3).

[0032] From this state, by dividing the intrusion into 100 stages atintervals of 0.1 second, the load that is applied to the indenter wasgradually increased until the load became 20 mN (from the point A to thepoint B in FIG. 2). In FIG. 2, the point B represents the time of themaximum load F max (here 20 mN) applied, i.e. the time of the maximumdeformation. Under this load, the indenter was maintained as was for 60seconds, whereby the so-called “creep deformation” was caused to thesample (from the point B to the point C). In FIG. 2, the depth ofintrusion (C-B) μm represents the amount of creep deformation.Subsequently, the indenter was raised in 40 stages at intervals of asecond until the minimum load of the tester (0.4 mN) was reached (fromthe point C to the point D). Further, in the state of that minimum loadof the tester (0.4 mN), the indenter was maintained as was for 60seconds (from the point D to the point E). In FIG. 2, the depth ofintrusion (D-E) μm represents the amount of creep deformation at thetime of the minimum load applied; the depth of intrusion (E-A) μmrepresents the residual amount of deformation; and further the depth ofintrusion (hmax-E) μm represents the restored amount of deformation.

[0033] The reason for applying the load to the sample resin compositionthrough the use of the ball indenter is that of the combination of thelenticular lens and Fresnel lens the crushed portions are the portionsof point contact wherein the lenticular lens configuration is verticallylaid and the Fresnel lens configuration is horizontally laid, and thattherefore the point load can excellently reproduce the actualphenomenon. Also, the reason whey the maximum load Fmax has been set tobe 20 mN is that because the pressure contact between the both lenses isconsiderably low and the actual measurement thereof is difficult, therequirement for causing, at the maximum amount of deformation, thereference resin to deform to an extent of 10 μm due to the displacementof it has been set as the maximum magnitude of load. The reason forhaving made the maximum amount of deformation approximately 10 μm or sois based on the opinion (refer to the paragraph “0018” in thespecification of Japanese Patent Application Laid-Open Publication No.2000-155203) of “the amount of deformation of the lens ordinarily has apermitted deformation of up to 0.01 mm at its outer-peripheral partbecause the lens even at that time does not permit any light from thelight source to pass therethrough” disclosed in that specification.

[0034] (4) Measuring Items

[0035] The parameters for specifying the mechanical properties of theresin composition in the present invention, i.e. the elastic modulus (E)and the creep deformation factor (C) are the ones that can be analyzedfrom the above-described load displacement loop (FIG. 2). Here, theprocedure under the preceding item was repeated three times, whereby theelastic modulus (E) and creep deformation factor (C) that were obtainedas the measuring items each time had their values averaged toarithmetical-mean values. Thereby, these values were recorded as themeasured values.

[0036] The elastic modulus (E) and the creep deformation factor (C) areexpressed as follows.

[0037] (a) Elastic Modulus: E$E = {{1/\left( {{2{\left( {{hr}\left( {R - {hr}} \right)} \right)^{\frac{1}{2}} \cdot \left( {h\quad \max} \right)}\Delta \quad {h/\Delta}\quad F} - {\left( {1 - {vw}} \right)/{Ew}}} \right)}\quad = {1/\left( {{{5.586 \cdot {hr} \cdot \left( {h\quad \max} \right)}\Delta \quad {h/\Delta}\quad F} - {7.813 \times 10^{- 7}}} \right)}}$

[0038] where hr represents the intersection (the unit: mm) of thetangential line to the load displacement curve with the intrusion-depthaxis when the testing load is maximum (the region of decrease in load,the region enclosed by the points C, D, and hmax in FIG. 2).

[0039] Also, Δ hmax/Δ represents the inverse rise in the loaddisplacement curve when the testing load is maximum (the region ofdecrease in load, the region enclosed by the points C, D and h max inFIG. 2). The unit is mm/N.

[0040] Further, νw represents the Poisson's ratio (=0.22) of thetungsten carbide; Ew represents the elastic modulus (5.3 ×10⁵ N/mm²) ofthe tungsten carbide; and R represents the radius (0.4 mm) of the ballindenter.

[0041] Just for reference, the elastic modulus E in the case of havingused the Vickers indenter (diamond) is expressed as follows.

E=1/(4 tan(2/α)hr·(hmax)Δh/ΔF/ρ ^(1/2)−(1−νdia)/Edia)

[0042] where α represents the apex angle of the Vickers indenter that is136°; ν dia represents the Poisson's ratio (=0.25) of the diamond; andEdia represents the elastic modulus (1.2×10⁶ N/mm²) of the diamond.

[0043] (b) Creep Deformation Factor: C

C=(h 2−h 1)·100/h 1

[0044] where h1 represents the depth of intrusion when the load hasreached the testing load (here 20 mN) maintained at a fixed value (thepoint B in FIG. 2); and h2 represents the depth of intrusion after thelapse (the point C in FIG. 2) of a predetermined length of time (60seconds) while that testing load is maintained as is. The unit is mm.

[0045] (5) Evaluation on Crush: The Fresnel lens sheet that has beenmolded from the ionizing radiation curable resin composition the elasticmodulus (E) and creep deformation factor (C) of that were measured abovewas jointly combined with a predetermined piece of lenticular lenssheet, and four sides thereof were fixed using a tape. Then eachassembly was fitted into a corresponding different TV size of woodenframe and was made up into a TV set, the white screen of which wasobserved with the naked eyes. After the lapse of one hour, the Fresnelsheets each of that was crushed was recorded as the mark “” while theFresnel lens sheets each of that was recognized as being free of crushwas recorded as the mark “◯”. (See FIG. 4).

[0046] (6) Test results: The elastic modulus (Y) and creep deformationfactor (C) of each ionizing radiation curable resin composition and theon-crush evaluated results of the Fresnel lens sheets each molded from acorresponding one of ionizing radiation curable resin compositions arecollectively shown in Table 1. Also, with the elastic modulus (E) andcreep deformation factor (C) being plotted along the abscissa andordinate axis, the on-crush evaluated results of test are represented asthe mark “◯” and “” as above, which are shown in FIG. 4. TABLE 1refractive index elastic creep evaluation (23° C., modulus deformationon Sample number D rays) (MPa) factor (%) crush 1 1.553 759.3 43.87 ◯ 21.553 1290 16.98 ◯ 3 1.553 814.5 19.75 ◯ 4 1.553 1729 12.11 ◯ 5 1.5522186 0.77 ◯ 6 1.553 1618 13.55 ◯ 7 1.551 458.6 58.68  8 1.551 745.540.51 ◯ 9 1.551 885.9 19.79 ◯ 10 1.551 1126 19.65 ◯ 11 1.551 725.6 60.79 12 1.551 830.4 33.84 ◯ 13 1.551 1347 12.00 ◯ 14 1.553 2733 −1.000 ◯ 151.553 1788.4 17.10 ◯ 16 1.553 3365 −5.654 ◯ 17 1.551 286.5 65.31  181.551 216.9 57.56 ◯ 19 1.551 251.8 66.25  20 1.551 307.4 64.31  211.551 1100 57.85  22 1.550 922.5 47.24  23 1.550 691.3 72.27  241.552 647.2 60.37  25 1.552 817.5 63.65  26 1.552 321.6 59.38  271.552 538.0 72.16  28 1.553 585.2 73.27  29 1.551 837.4 76.48  301.552 411.85 31.531 ◯ 31 1.550 132.2 26.81 ◯ 32 1.553 79.58 23.25 ◯ 331.552 190.0 21.30 ◯ 34 1.551 95.29 8.859 ◯ 35 1.550 128.0 130.89  361.550 37.8 3.03 ◯ 37 1.552 118.36 14.56 ◯ 38 1.552 392.2 55.0 ◯ 39 1.551183.4 33.83 ◯

[0047] (7) Analysis of Test Results: The inventor of this applicationmade his analysis of the above-described test results and as a resultcame to the following perceived conclusion. First, he classified thetested ionizing radiation curable resin compositions into a group ofones the elastic moduli of that each are low (soft) and the other groupof ones the elastic moduli of that each are high (hard). And he hasfound out that, in the case of the soft group, it is possible to obtainthe lens having no problems with crushes when the elastic modulus E ismade greater than 0 MPa and smaller than 840 MPa and the creepdeformation factor is made greater than 0% and smaller than 57%, orpreferably greater than 3% and smaller than 55%, or most preferably whenthe elastic modulus E is made greater than 38 MPa and smaller than 412MPa and the creep deformation factor is made greater than 3% and smallerthan 55%. Also, in the case of the hard group, he has found out that thelens having no problems with the crushes can be obtained when theelastic modulus is made greater than 840 MPa and smaller than 3500 MPawhile the creep deformation factor is made greater than −10% and smallerthan 20%, or more preferably made greater than −6% and smaller than 20%.

[0048] Also, he has found out that with attention being directed onlytoward the relationship between two of the elastic modulus E and creepdeformation factor C of the ionizing radiation curable resincomposition, if using for molding the ionizing radiation curable resincomposition having the relationship of C<−2×10⁻²E+63 and C>−2.6×10⁻³E+3(the area enclosed by the straight lines m, n and E=0 in FIG. 5), it ispossible to obtain the lens having no problems with the crushes.

[0049] Incidentally, in the foregoing description, an explanation hasbeen given of the ionizing radiation curable resin composition that isused to mold the Fresnel lens sheet used for the projection screen incombination with the lenticular lens sheet. However, the technical ideaof the invention of this application is not limited to that but can beapplied to any optical lens that is molded from other resin composition,the forward end in the lens configuration of that sharpens, and theforward end portion of that receives pressure in the direction of itsbeing crushed.

[0050] Also, the present invention is not limited to the above-describedembodiment but permits suitable changes to be made without departingfrom, or running counter to, the subject matter or idea of the presentinvention readable from the scope of the claims and the entirespecification. Resin compositions for lens sheet, the lens sheets, andprojection screens resulting from such changes are also included in thetechnical scope of the present invention.

INDUSTRIAL APPLICABILITY

[0051] As has been explained above, by setting the elastic modulus E andcreep deformation factor C of the ionizing radiation curable resincomposition each to within a range between predetermined values with thepressures actually received and the time factors being taken intoaccount, even when any pressure has been applied to the surface of thelens sheet having been molded from that ionizing radiation curable resincomposition, it is possible to obtain excellent images without causingany crush of the lens configuration.

1. An ionizing radiation curable resin composition, the ionizing radiation curable resin composition forming a lens portion of a lens sheet, wherein a compression modulus of elasticity is greater than 0 MPa and smaller than 840 MPa; and a creep deformation factor is greater than 0% and smaller than 57%.
 2. An ionizing radiation curable resin composition, the ionizing radiation curable resin composition forming a lens portion of a lens sheet, wherein a compression modulus of elasticity is greater than 840 MPa and smaller than 3500 MPa; and a creep deformation factor is greater than −10% and smaller than 20%.
 3. An ionizing radiation curable resin composition, the ionizing radiation curable resin composition forming a lens portion of a lens sheet, wherein, when E (MPa) represents a compression modulus of elasticity and C (%) represents a creep deformation factor, the ionizing radiation curable resin composition has a compression modulus of elasticity and creep deformation factor that have a relationship of C<−2×10⁻² E+63 and C>−2.6×10⁻³ E+3
 4. A Fresnel lens sheet having a lens surface formed of the ionizing radiation curable resin composition as described in one of claims 1 to
 3. 5. A projection screen equipped with the Fresnel lens sheet as described in claim
 4. 